Organization and Basis of Presentation - Narrative (Details) $ in Thousands	12 Months Ended
	Apr. 30, 2018 USD ($) subsidiary segment	Apr. 30, 2017 USD ($)	Apr. 30, 2016 USD ($)
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of operating subsidiaries | subsidiary	2
Number of reportable segments | segment	1
Net loss	$ 1,476	$ 6,884
Accumulated deficit	70,826	69,350
Negative working capital	2,400
Cash and cash equivalents	$ 856	$ 3,295	$ 2,585